The Importance of Precessional Signatures in the Tropical Climate

The presence of orbital frequencies in the paleoclimate record is well established. The mechanisms that link the orbital forcing with climate, however, remain poorly understood. In this paper, we focus on climate change on orbital timescales in the tropics. Experiments with an atmospheric general circulation model are used to investigate the response of the tropical climate to precessional forcing. These results are compared with the tropical response to Last Glacial Maximum forcing. We find that while the glacial forcing has a large tropical mean signal in temperature, the precessional response of the hydrological cycle and atmospheric circulation are at least as large as that of the glacial, and at times of large eccentricity may overwhelm the glacial signal. These results emphasize the different nature of changes associated with the 100 kyr cycle of glaciation and the direct response to orbital forcing. Examples are given to show how these results can offer quantitative aid in deciphering these signals in tropical paleoclimate records.